1. Field of the Invention
The present invention relates to novel dehydrated, essentially anhydrous mixtures of rare earth halides and alkaline earth or alkali metal halides and to a process for the production thereof.
This invention more especially relates to admixtures of rare earth halides and alkaline earth or alkali metal halides of the chloride, bromide or iodide type, comprising a very low percentage of water and a very low amount of rare earth oxyhalide values.
2. Description of the Prior Art
The rare earth halides are typically produced in an aqueous medium, for example by acid digestion of a rare earth oxide in an aqueous medium.
Thus, the halides produced, with the exception of the fluoride, are hydrated halides comprising a number of molecules of water, typically from 3 to 9 per molecule of halide.
This structural water is deleterious in certain applications or end uses of the halides, such as, for example, chemical or electrochemical reduction processes for the production of metal, e.g., the production of neodymium or of an alloy of neodymium with other metals.
Many processes for the dehydration of these hydrated rare earth halides have been proposed to this art.
Thus, V. W. Wendlandt, in J. Inorg. Nucl. Chem., 5, 118 (1957), describes the thermal decomposition of hydrated rare earth chlorides. Such dehydration allows the halide monohydrate to be obtained. However, the removal of this last molecule of water requires heating to a temperature above 200.degree. C. At this temperature, rare earth halides are converted into the oxyhalides. The presence of these oxyhalides also adversely affects the metal production processes referred to above.
Dehydrating processes have also been proposed to this art employing a dehydrating agent such as hydrogen halides, ammonium halides, carbon tetrachloride, phosgene or SOCl.sub.2, as well as the halogens. The processes described especially by Matignon (C.R. accord. Sci., 134, 427 (1902)) and Kleinheksel and Kremers (JACS, 50, 959 (1928)) entail passing a gaseous stream of a dehydrating agent over the hydrated halide. However, these processes do not permit lowering the concentration of water and/or of oxyhalide to low values, especially when the mass of rare earth halides to be dehydrated is large.
Such processes cannot, therefore, be carried out on an industrial scale.